Method for projectile velocity measurement



Nov. 2, 1965 s. E. SIMS ETAL 3,215,932

METHOD FOR PROJECTILE VELOCITY MEASUREMENT Filed Oct. 21. 1960 2 Sheets-Shet 1 PICK UP PICK up MAGNETIZING COIL GUN i l0 l2 I4 zsvoc START STOP 2o WAVE SHAPING T ADAPTER $52 RECORDING CHRONOGRAPH DIGITAL ss RECORDER Eigl JAMES RINIMFZYAIRAORS WILLIAM A. NORTHINGiTON WILLIAM TOOL BY SAMUEL E sl Nov. 2, 1965 s. E. SIMS ETAL METHOD FOR PROJECTILE VELOCITY MEASUREMENT Filed Oct. 21 1960 2 Sheets-Sheet 2 m m m T N m um Vl m mmmm m R.A. W L Mum ww n n5m mm Om '3' mm 5 32 5 8E InEEQOZOKIU 0t 7 United States Patent 3,215,932 METHOD FOR PROJECTILE VELOCITY MEASUREMENT Samuel E. Sims, Shalimar, William A. Northington, Fort Walton Beach, William Toole, Point Washington, and James R. Milam, Gainesville, Fla., assignors to the United States of America as represented by the Secretary of the Air Force Filed Oct. 21, 1960, Ser. No. 64,000 1 Claim. (Cl. 324-70) The present invention relates to a method for measuring the velocity of projectiles and is more particularly concerned with a method for obtaining the velocity of a projectile without magnetizing same prior to the firing.

One of the principal systems for measuring the velocities of projectiles in the prior art involves magnetizing the projectile and firing the projectile through sensor loops which respond to the passage of the projectile in such a way as to allow the calculation of the projectiles velocity. This prior art system requires that the projectile be delinked from its belt, magnetized, and relinked before firing. In handling large numbers of rounds for burst velocity measurements, the prior art system consumed a great deal of time. Further, modern projectiles tend to have a high percentage of nonferrous metals alloyed into them. This high alloy content has reduced the magnetic retentiveness for such projectiles and, accordingly, the allowable time between magnetization and firing.

It is thus an object of this invention to provide a projectile velocity measuring apparatus of the electromagnetic type which does not require the magnetization of the projectiles prior to their firing.

It is a further object of this invention to improve on projectile velocity measuring apparatus of the electromagnetic type by providing a means which magnetizes the projectile while in motion in coaxial spaced relation with sensor loops wherein an electrical pulse is generated in each sensor loop by the passage of the projectile through the successive loops from which time interval the velocity of the projectile can be determined.

The nature of the invention, further objects and advantages will appear more fully by consideration of the embodiment illustrated and from the accompanying drawing hereinafter to be described.

In the drawings:

FIGURE 1 is a schematic illustration of an embodiment of the novel velocity coil system, and

FIGURE 2 is a circuit diagram of the wave shaping adaptor.

Referring now to FIGURE 1 of the drawing, one form of the invention comprises three loops 10, 12 and 14 arranged in spaced coaxial relation and encircling the path of a bullet or projectile fired from gun 16. The first loop is the magnetizing loop and is formed of multiple turns of wire in sufiicient number that when 28 volts direct current is applied to it, a projectile passing through the loop will be magnetized. The remaining two loops 12 and 14 are wound, dimensioned and constructed alike of multiple turns of wire and appropriate insulation and are the sensor or pickup means for the system.

Firing the projectile through the magnetizing loop 10 magnetizes the projectile. The now magnetized projectile passes through sensor loops 12 and 14 which induces a voltage in the coil of each loop.

Referring now more particularly to FIGURE 2, a wave shaping adaptor 20 connected to sensor loops 12 and 14 in series or parallel through input lines 18 and 19, accepts the sinusoidal signals generated in the coil of each loop. The signals pass through the polarization switch 22 to the amplifier portion of the wave shaping adaptor. The

3,215,932 Patented Nov. 2, 1965 ice.

polarization switch allows the output from the sensor loops to be properly polarized with respect to the magnetized projectile. The amplifier is composed of three push-pull stages 26, 28 and 30. The first two stages are degenerative to line-to-ground noise. The amplifier has a relatively flat response from 10 c.p.s. to 40 kc.p.s. and has a nominal gain of 1300.

Clipping, integrating, diiterentiating and gate circuits are provided to sharpen the input pulse and also assist in noise discrimination. The clippers cut off the top and bottom peaks and permit additional amplification of the center portion of the pulses. Two stages 32 and 34 of clipping are provided and each stage is followed by a stage of gain, the lower portion of tube 36 and the upper portion of tube 38, respectively. After the second stage of gain, the signal is dilferentiated to produce a sharp, positive spike. The differentiating is accomplished by capacitor 47 connected to the anode of the upper half of tube 38 cooperating with resistor 49 connected from the control grid 42 of tube 40 to ground. This spike is applied to the control grid 42 of gate tube 40. The gate tube 40 is biased so that the anode grid 44 prevents the tube from conducting despite the sharp pulse applied to the control grid. The output of the first three stages of the amplifier is also applied to an integrating network 48. This signal is integrated and passed through a stage of amplification in the lower half of tube 36. The resulting signal is a positive pulse. This pulse is applied to the anode grid 44 of gate tube 40, which causes the tube to act as a gate. The output of this gate tube 40 is amplified in the lower half of tube 38 which provides an output pulse suitable for timing.

The time constant of the integrating network 48 is variable by means of switch 50. This permits setting the network so that the integrated signal will just gate the gate tube 40. Since the noise is primarily high frequency, the integrating circuit shunts this noise and thus serves to stabilize the instrument.

The shaped signals then pass through line 52 to counterchronograph 54. The counter-chronograph is of conventional design such as Potter, model 3054, and measures the time required for the projectile to travel from the sensor coil 12 to the sensor coil 14. This time is then printed on tape in the digital recorder 56, which is of conventional design such as Potter, model 960. It will be appreciated that the instant invention otters a method for obtaining the time of travel of projectile between coils 12 and 14 electronically so as to reliably and accurately determine the velocity of the projectile from its travel time and the distance between the two known points.

Although but a single embodiment of the invention has been shown and described, it will be apparent to those skilled in the art that many other forms thereof, as well as changes in that described, are possible.

We claim:

The method of measuring the velocities of projectiles fired from a gun comprising the steps of: firing a projectile from a gun; magnetizing said projectile at. a first point as it travels substantially at muzzle velocity; producing a first electrical signal in response to a magnetic field of said projectile as it passes a second point beyond said first point and while said projectile travels substantially at muzzle velocity; producing a second electrical signal in response to the magnetic field of said projectile as it passes a third point beyond said second point and while said projectile travels substantially at muzzle velocity; applying said first and second electrical signals to time measuring means to thereby indicate the time of travel of said projectile between said second and third points; and com puting the velocity of said projectile from said time of 3 4 travel and the distance between said second and third 2,617,023 11/52 Weller 324-70X points. 1 2,959,734 11/60 Marsh et a1 324-68 OTHER REFERENCES References Clted by the Examiner Measuring Projectile Velocity, Electronic Industries,

UNITED STATES A S a OCtObBI 1943, pages 66, 67 and 196.

2,400,189 5/46 Carlson et aL 324 7O WALTER L. CARLSON, Primary Examiner.

2,444,751 7/48 Scott 324-34 X SAMUEL BERNSTEIN, FREDERICK M. STRADER, 2,558,249 6/51 Hewlett et a1. 324-68 Examiners. 

